1. Field of the Invention -- This invention relates to a photoconductive composition, an imaging member provided with an imaging layer of the above photoconductive composition, and an imaging method. More specifically, this invention concerns a photoconductive composition possessing good ambipolar discharge characteristics which can be readily formed by standard fabricating techniques into photoconductive films useful in electrostatographic imaging.
2. Description of the Prior Art -- The formation and development of images on the imaging surfaces of photoconductive materials by electrostatic means is well known. The best known of the commercial processes, more commonly known as xerography, involves forming a latent electrostatic image on an imaging surface of an imaging member by first uniformly electrostatically charging the surface of the imaging layer in the dark and then exposing this electrostatically charged surface to a light and shadow image. The light struck areas of the imaging layer are thus rendered conductive and the electrostatic charge selectively dissipated in these irradiated areas. After the photoconductor is exposed, the latent electrostatic image on this image bearing surface is rendered visible by development with a finely divided colored electroscopic material, known in the art as "toner". This toner will be principally attracted to those areas on the image bearing surface which retain the electrostatic charge and thus form a visible powder image.
The developed image can then be read or permanently affixed to the photoconductor where the imaging layer is not to be reused. This latter practice is usually followed with respect to the binder-type photoconductive films (e.g. ZnO) where the photoconductive imaging layer is also an integral part of the finished copy.
In so-called "plain paper" copying systems, the latent image can be developed on the imaging surface of a reusable photoconductor or transferred to another surface, such as a sheet of paper, and thereafter developed. When the latent image is developed on the imaging surface of a reusable photoconductor, it is subsequently transferred to another substrate and then permanently affixed thereto. Any one of a variety of well known techniques can be used to permanently affix the toner image to the copy sheet, including overcoating with transparent films, and solvent or thermal fusion of the toner particles to the supportive substrate.
In the above "plain paper" copying system, the materials used in the photoconductive layer should preferably be capable of rapid switching from insulative to conductive to insulative state in order to permit cyclic use of the imaging surface. The failure of a material to return to its relatively insulative state prior to the succeeding charging sequence will result in a decrease in the maximum charge acceptance of the photoconductor. This phenomenon, commonly referred to in the art as "fatigue", has in the past been avoided by the selection of photoconductive materials possessing rapid switching capacity. Typical of the materials suitable for use in such a rapidly cycling system include anthracene, sulfur, selenium and mixtures thereof (U.S. Pat. No. 2,297,691); selenium being preferred because of its superior photosensitivity.
More recently, a number of organic photoconductive compositions have also been developed which reportedly possess the requisite speed and spectral response to provide commercially acceptable imaging surfaces; e.g. U.S. Pat. Nos. 3,037,861 and 3,484,237. Some of the principal advantages of these polymeric compositions over the traditional inorganic materials used in electrophotography are the relative ease of fabrication, comparatively low cost and inherent flexibility. Most such polymeric photoconductive materials, however, are not competitive with inorganic materials such as selenium with respect to their photosensitivity. The term "photosensitivity" is used throughout this disclosure to describe the relative rate of photoinduced discharge of a surface charge on an imaging layer of these materials; the more rapid its rate of photoinduced discharge, the more photosensitive a material. A number of organic materials are known to possess high light sensitivity, however, cannot be readily formed into coherent photoconductive films. The use of such intractable materials is possible but requires their dispersion in a host vehicle for fabrication of an imaging layer having the requisite physical and mechanical properties. Poly(9,10-dimethylene-anthracene) falls into this latter class of photoconductive materials. Typical of the teachings for the use of this material is U.K. Pat. No. 1,101,391 where this polymer is disclosed in a binder type photoconductive imaging layer. Where a polymeric material is physically dispersed throughout a binder as disclosed in the above noted British patent, its photosensitivity or rate of photoinduced discharge is concentration dependent. In other words, in order to enhance the rate of photoinduced discharge of a surface charge in such binder type films, additional amounts of polymeric photoconductive materials must be dispersed therein. As the concentration of this dispersed photoconductive material increases, the physical and mechanical properties of such films are usually adversely affected.
It is thus the object of the invention to remove this as well as related deficiencies in the prior art.
More specifically, it is an object of this invention to provide a photoconductive composition capable of ready fabrication into an imaging layer.
Another of the objects of this invention is to provide a photoconductive composition having good ambipolar photodischarge characteristics.
Still yet another of the objects of this invention is to provide an easily molded photoconductive composition from highly intractable photoconductive materials.
Further objects of this invention involve the use of the above photoconductive composition as an integral component of an imaging member and the further use of said imaging member in an imaging method.